This invention relates to an internal combustion engine, particularly to a gas injection system for an internal combustion engine of a motor vehicle.
In conventional internal combustion engines for motor vehicles, since opening of a throttle valve is low and an amount of sucked air is small during idling and light loaded driving of the engine, the velocity of flow of the air-fuel mixture entering from an intake manifold into a cylinder is low at a suction stroke of the engine, thus a swirl produced in the cylinder is weak. As a result, during ignition which is normally taken place at the end of the compression stroke of the engine, the swirl of the mixture retained in the cylinder becomes weaker, so that firing and combustion of the mixture are not adequate. To ensure stable driving of the engine, it is necessary to supply a mixture having an air-fuel ratio which is lower than that of the mixture supplied during medium or high loaded driving of the engine, that is, the richer mixture is required. This results in an increase of fuel consumption as well as increase of amounts of carbon monoxide (CO) and hydrocarbon (HC) contained in exhaust gas due to imperfect combustion of the richer mixture.
Recently, there has been proposed to burn a mixture much leaner than the stoichiometric mixture in order to reduce the amount of CO and HC, particularly the amount of nitrogen oxide (NO.sub.x) contained in the exhaust gas. Also, there has been proposed to draw a portion of exhaust gas from an exhaust system of the engine and to mix and burn it with the mixture in the cylinder to reduce the amount of NO.sub.x in the exhaust gas. However, in both cases, firing and combustion of the mixture become insufficient, so that drivability and rate of fuel consumption become worse.
To avoid the above drawbacks, there has been developed an internal combustion engine comprising a combustion chamber having an inlet port connected to a main intake passage in which a throttle valve is mounted, a spark plug having a spark gap facing into the combustion chamber, an injection bore provided near to said spark gap for injecting gas into said combustion chamber in a predetermined direction, and a secondary intake passage connected to the injection bore through a secondary inlet valve. In this arrangement, the gas is strongly injected from the injection bore into the combustion chamber during a suction stroke of the engine. This flow of gas provides a mixture supplied to the combustion chamber with a strong swirl or turbulence and also clears off the combustion gas existing around the spark gap to improve firing and combustion of the mixture, thereby extending a limit of combustion of the lean mixture and improving the fuel consumption and the drivability.
However, the engine of this type has a disadvantage that an area around the spark gap of the plug is over-cooled, since a large amount of the gas from the secondary intake passage is injected into the combustion chamber during idling or extremely light loaded driving of the engine. This results in insufficient firing of the mixture to cause misfiring and to have the motion of the engine instabilized during the idling and extremely light loaded driving.